“I just booted up Origin today to play BF3 and I see Dead Space 2 there. Why? I bought this game on Steam four months ago. I just beat it last week and haven't booted it up since. The purchase date in Origin states Feb 18, 2012 (today). The CD keys match.”

Another read:

“Yep did the same to me with Dead Space and Mass Effect 2.”

The claim that “the CD keys match” would suggest EA can access and use certain Steam data to reference what games its Origin customers have purchased elsewhere.

It is unclear if or when Valve sanctioned EA access to such data. It could have been a term in its original publishing contract, or later on when EA established the Origin portal.